A cloaker can try to wrap a Medium or smaller creature in its body as
a standard action. The cloaker attempts a grapple that does not
provoke an attack of opportunity. If it wins the grapple check, it
establishes a hold and bites the engulfed victim with a +4 bonus on
its attack roll. It can still use its whiplike tail to strike at other
targets.

Attacks that hit an engulfing cloaker deal half their damage to the monster and half to the trapped victim.

The Tactics section says Engulf is usually used versus a lone opponent, but it seems like the main danger of it comes only when you have other party members hitting the cloaker. The bite deals 1d4+2 damage, and is far from an auto-hit. (I believe the "+4 bonus on its attack roll" phrasing means "it attacks using its bite as its primary weapon at +8, taking the -4 penalty for attacking with a natural weapon in grapple, for a total to-hit of +4".)

This is going to take forever to kill anyone unless the cloaker is dealing some kind of unarmed strike damage with its grapple checks as well (and if it did, they could have given it Constrict). Is the idea that you engulf and then moan instead of using the bite attack? Using unnerve or stupor to make the target helpless will let you kill it a whole lot faster than 1d4+2 damage a round.

2 Answers
2

The description reads (to me, disclaimer as per) that the bite is a triggered (and ongoing) action at a total of +7 to attack (bite 3, bonus 4) as a consequence of the grapple. The grapple attack is at +13 (Listed on it's info) which then immobilises the target and is followed thereafter by biting immediately and every following round at +7.

This does mean that a lone target is going to have to break the grapple before they can do any significant damage while the cloaker grapples and keeps doing damage, since the grapple skill allows further opposed grapples to do damage as well as the cloakers bonus biting attack. I can't see where damage for the opposed grapple is specified, but I use base unarmed (size based, d2 small, d3 medium, etc) plus strength bonus for the creature, which would make it more than it's bite! But as you say, they could have just given it engulf instead of this and it seems a somewhat strange omission given the visual aspect of what the creature is doing.

In the mean time the victim can fight back and hurt the cloaker, but their attack is at -4 and they'll only be dealing unarmed base damage, unless they're a monk (the bane of the cloaker) or have a light weapon to hand. grapple info

Although it's not high damage it does screw up spellcasters as they'll be very restricted in what they can cast in return, so it sounds like a good way to get that mage that's been throwing fireballs around and cackling to me ;)

I think the point of engulf may be that it doesn't get saved against like other abilities, meaning that people with freakish saves and low BAB can be easily engulfed rather than having to worry about saves; engulf functions more on a long term scale than the moan effects, and such.

Alternatively, there could be a goal of modeling a behavior which isn't necessarily based off of efficiency but rather instinct; engulf may be a part of the cloaker's sustenance or such and be a behavioral action rather than one of cold calculation. Ultimately, I'd say it's the Dungeon Master's discretion. The damage to an engulfed character is merely to reflect the fact that the cloaker is around them, included for cases of sneak attacks or reinforcements (and the like) in this case.